Air force ensign

Ensign is the national flag flown on a vessel to indicate nationality. The ensign is the largest flag, generally flown at the stern (rear) of the ship. The naval ensign (also known as war ensign), used on warships, may be different from the civil ensign (merchant ships) or the yacht ensign (recreational boats). Large versions of naval ensigns called battle ensigns are used when a warship goes into battle. The ensign differs from the jack which is flown from a jackstaff at the bow of a vessel.

In its widest sense, an ensign is just a flag or other standard. The European military rank of ensign, once responsible for bearing a unit's standard (whether national or regimental) derives from it (in the cavalry the equivalent rank was cornet, named after a type of flag). In contrast, the Arab rank of ensign, liwa, derives from the command of a unit or units with an ensign, not the carrier of such a unit's ensign, and is a general officer. In Arab armies, "ensign" is a unit title equivalent to a Western brigade, and as a rank is equivalent to a divisional commander.

In nautical use, the ensign is flown on a ship or boat to indicate its appartenance. While this includes its nationality, it may well indicate more information (e.g. civilian, naval, or police vessel) rather than being the national flag itself. This is particularly common for commonwealth and European countries.

Ensigns are usually at the stern flagstaff when in port, and may be shifted to a gaff (if available) or mast amidships when the ship is under way, becoming known as a steaming ensign.

Vexillologists distinguish three varieties of a national flag when used as an ensign:

Many countries do not distinguish between these uses, and employ only one national flag and ensign in all cases; in the United States, for example, all ships of the seagoing services of the United States Government with the exception of the United States Coast Guard fly the national flag as their ensign, although the ships of some agencies also fly an agency flag as a "distinguishing mark." Other countries (like the United Kingdom, Ukraine, Italy, Russia, South Africa, Australia, New Zealand, and Japan) use different ensigns. Such ensigns are strictly regulated and indicate if the vessel is a warship, a merchant ship, a ship under contract to carry mail, or a yacht, for example.

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